Process of separating the constituents of mineral silicates



May il@ is. w. SCOFIELD ET AL' PROCESSOF SEPARATING THE CONSTITUENTS OF MINERAL -SILICATES Filed May 1'7 5.5. 5.2.5.5 Gbs :E565 ...Eri

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Patented May (i3, llQl.

' narran sraras SHERMAN W. SCOFIELD AND JOHN-2B. LA RUE, OFVCLEVELAND, OHO; SAID iA RUE parlar oratori.

ASSIGNOR TO SAID SCOFELD.

EROCESS 0F SEPRATING THE CONSTITUENTS MNERAL SILSCCATES.

Application filed May 17,

To all 'who/m t 'may concern.'

Be it known that we, SHERMAN W. SCO- rtELD and JOHN B. LA RUE, citizens of the United States, residents of Cleveland, county of Cuyahoga, and State of Chio, have invented new and useful .Improvements in Processes of Separating the Constituents of Mineral Silicates, of which the following is a specification, the principle of the invention being herein explained andthe best mode in which we have contemplated apply-- ing that principle, so as togdistinguish it from other' inventions.

Our invention relates to processes for .separating the constituents of mineral silicates, and'particularly to processes for eX- tracting the potassium and other values from potash feldspar. This invention relates to improvements in a process of this general character disclosed in our pending application for U. S. Letters Patent, Serial No. 407,724.

The annexed drawing and the following description set forth in detail certain steps` embodying. our invention, the disclosed steps, however, constituting but one o'f the.

various methods in which the principle ,ot the said invention may be carried out.

Thedrawing represents a flow diagram of our improved process. Y

` Wel first crush high grade crystalline potash-feldspar to about thirty-live mesh, in order that a subsequent calcining can be thoroughly and economically effected.v `We then calcine this crushed'V ore until the same is converted to an amorphous condition, in order vthat a subsequent digestion with caustic potash may be effected to convert the ore constituents into water soluble or acid soluble compounds. This calcining is eilected upon the bed of a furnace or in any other suitable manner by heating from one (l) to two (2) hours at from 800o to 10500 C. After the ore has -thus been reduced to an amorphous condition, we then further crush thesame to about two hundred (200) mesh after which the same is 'digested with the caustic potash. rlhe digestion of the ore with caustic potash is not carried to a point where all of the ore is converted into water soluble potassium silly cate and potassium z tluininate but there is also produced a water insoluble but an acid soluble potassium aluminum silicate. We'

1922, serial no. $61,704.

.use 90% caustic -potash for the allalicdigesvand also an equal amount of water, heating forfroni one (1) to two hours at a temperature from 275` to 325 C. The operation is effected in an autoclave at a pressure .of from 300 to 350 lbs. per square inch. )Ve then allow a further reaction period of about two (2) hours, resulting in a complete decomposition of the ore into the water or acid soluble compounds above-mentioned. During the digestion operation considerable hydrogen isiformed, after the temperature has reached substantially 200 C., due-to the tact that the iron walls ofthe autoclave are attacked by the strong caustic potash, the reaction being Fe-l-QKGHZFMOlQg--Hg. It may be that some impurity in the ore or even in the iron acts as a catalyst for this reaction. The iron `later appears as an impurity in the aluminum salts or possibly in the silica. In order that this envolved hydrogen may not form an explosive mixture witlr'the oxygen of the air-#which is in the autoclave at the start, we remove this air from the autoclave during the'tirst part 'of the' digestion operation by allowing the pressureto reach thirty (30) to forty (40) lbs. per square inch and then allowing the oxygen toxv escape from the autoclave. The alreadyl formed steam displaces the air which escapes and finally the interior of the auto clave contains nothing but steam, indicated by a current of pure quickly condensingr steam escaping from the autoclave valve.

lVe dilute the alkali digestion products with from one (l) to four (4) times their volume of water and then carbonate themixture with carbon dioxide, maintaining a pressure of about 22 inches above atmospheric pressure, the temperature being maintained at substantially room temperature ,by f

means of apositive removal of the generated heat. `We thus obtain the water soluble potash value in solution and precipitate aluini num hydroxide and ortho silicic acid The mass action resulting from the pressure above-mentioned and the Amaintenance et normal temperature effects the carbonating in about fortydive (45) minutes, the same taking place in two stages, the first stage resulting in a conversion of the potassium content to potassium carbonate and taking i mal carbonate.

only about tive minutes and the second stage convertin the potassium carbonate to bicarbonate and taking about forty (40) minutes. The reaction is based upon the action if the ionized acid (H2003) formed by the dissolving of C02 gas in Water. There is only incomplete precipitation of the silicon andaluminum during the first stage because the potassium carbonate being strongly Megane alkaline dissolves aluminum hydroxide `and lio ortho silicio acid and it is not'until this carbonate is very largely converted into bicaibonate, Which is almost neutral in reaction, that all of the aluminum and silicon separate out. The reactions are represented, at least in principle, by the following equations:

Of course, carbonation to formation of 100 per cent bicarbonate requires just twice the amount of C02 that is needed for the nor.-i The speed of carbonation can be greatly increased b distributing the gas uniformly over the W ole cross-section of the volume of liquid to obtain the most extensive Contact between the gas andliquor, and also .by vei strong agitation. To'the carbonation pro ucts We add about one-half of their volume of Water. We then repeatedly filter and Wash, the Wash Water re.- quirements being from tWo and onefquarter (2l) to 4 and one-half (4%) gallons of Water per lb. of feldspar digested. These steps, of course, result in the recovery of so much of the potassium from the feldspar as was converted into Water soluble compounds during the alkali digestion period.

, vWe convert only a part of the potassium ,carbonates thus obtained into sales products and the balance We causticize in order to obtain caustic potash for reuse in further digestion operations. In detail, We evaporate the carbonate solution in steps obtaining v each time a saturated solution from Which,

as the temperature is permitted to drop, crystalline masses of potassium carbonate and potassium bicarbonate are` obtained, preferably until from live to ten (10) per cent of the tot-al potassium content of the carbonate solution is removed. The potassium carbonatos thus obtained also contain the sodium carbonate that is present and thus prevent the building up of the sodium content during repeated reuses of the caus tic potash.v The balance of the carbonate solution is concentrated to a 10 percent solution Which is suitable for a causticizing operation withv lime to produce caustic potash for reuse andcalcium Acarbonate for sale.

To the alumina and silica residue produced by the carbonating We add enough' Water to make a slurry and then digest the same with from to 125 per cent excess of per cent sulphuric acid7 thus placing all the aluminum salts` in solution as alum and aluminum sulphate and rendering the freshly precipitated silica utterly insoluble as Si02, due to the dehydrating action of the sulphur'ic acid. l

The acid digestion products are diluted with Water and then the saine repeatedly filtered in an acid proof ilter and Washed, the Wash Water utilized being about 2.2 gallons per lb. of ore digested.

The aluminum salts in solution are l'ractionally crystallized, producing as a first. fraction practically pure alum containing only traces of iron, the successive fractions containing proportionately more iron and less alum and, of course, more aluminum sulphate. The alum is represented by the formula K2SO4A12(SO4)3.24H2O and the reason for its presence lies in the fact that there is Jformed in the autoclave a Water insoluble but acid decomposable silica containing KZO and the latter will not appear i'n the carbonate liquors, but in the residue of alumina and silica, there to be decomposed by the sulphuric acid treatment and thence to follow the aluminum.

The silica is dried of its absorbed and adsorbed Water and then cleansed from impurities by treatment With hot concentrated sulphuric acid for one or two hours and then `filtered and Washed free of acid.

What we claim is 1. In a process of separating the constituents of mineral silicates, the steps of recovering tlie potassium value consisting in,

first, converting the silicate into alkali-metal silicate and aluminate by means of a solution of caustic alkali; and then recovering the potassium by passing carbonio acid gas7 in the cold and under pressure additional to that normally incident to carbonation, through the silicate and aluminate solution.

2. ln the process of separating the constituents of mineral silicates, the steps of.. recovering the potassium value consisting in,

hrst, converting the silicate into alkali-metal" aaa-aow silicate and Valuminate by means of a so-lution of caustic alkali, and then recovering the potassium by passing carbonio acid 'gas throughthe silicate and aluminate solution, the heat generated by carbonation being positively removed and the carbonation being eiilected under va pressure of substantially 22 inches above atmospheric pressure.

3. In the process of separating'the' constituents of mineral silicates, the steps of recovering the potassium Value consisting in, first, converting the silicate into potassium sil-icate and aluminate by means of a solution of substantially ninety per cent (90%) caustic potash; and then recovering the potassium by passing carbonio acid gas, in the cold and under pressure additional to that normally incident to carbonation, through the potassium silicate and aluminate solution..

4. In a process of separating the constituents of mineral silicates, the steps which consist in converting the natural ore into an amorphous condition; digesting the same with substantially 90% caustic potash in amount from one and one quarter (19;) to two (2) times the Weight of the ore and ar. equal Weight of water, thus obtaining Water soluble potassium silicate and potassium aluminate and Water insoluble but acid solublepotassium aluminum silicate; diluting the alkali digestion products With Water and carbonating with carbon dioxide to remove the Water soluble potassium values; filtering and then digesting the alumina and silica residue with an excess of substantially 95% sulphuric acid to remove the aluminum as soluble salts; and filtering and fractionally crystallizing the aluminum solution, thus obtaining as a first fraction ractically `pure alum (K2SO4A12'(SO4)3.24 20) and successive fractions of alum containing increasing quantities of aluminum sulphate.

5. In a process of separating the constituents of mineral silicates, the steps Which consist in converting the natural ore into an amorphous condition; digesting the same with substantially 90% caustic potash in amount. substantially two (2) times the weight of the ore and an equal Weight of water, thus obtaining .Water soluble potassium silicate and potassium aluminate and water insoluble but acid soluble potassium aluminum silicate; diluting the alkali digestion products with an amount of Water at least equal in volume to said products,'and carbonating with carbon dioxide to substantially complete bicarbonation to remove the water soluble potassium values; filtering and thendigesting the alumina and silica residue With an excess of substantially 95% sulphuric acid to remove the aluminum as soluble salts; and se arating the resultant insoluble silica from't e solution of alumi` num Salts. v .f

6. In a process of separating the constituents of mineral silicates, the steps which consist in crushing the natural ore to substantially thirty-tive (35) mesh; converting the crushed ore to an amorphous condition; further crushing the amorphous ore to substantially two hundred (200) mesh; digesting the line ore With substantially 90% caustic potash in amount from one and one quarter (19g) to two (2) times the Weight of.

soluble but acid soluble potassium aluminum silicate; diluting the alkali digestion products with Water andcarbonating with carbon dioxide to remove the Water soluble potassium values; filtering and 'then digesting the alumina and silica residue With an excess of substantially 95% sulphuric acid to remove the aluminum as soluble salts; and iiltering and ractionally crystallizing the aluminum solution, thusobtaining as aiirst fraction practically pure alum (K2SO4A12 (SO4).24H2O) and successive fractions of alum containing increasing quantities 'of aluminum sulphate. A

7. In a process of separating the constituents of mineral silicates, the steps which consist in converting the natural ore into an amorphous condition digesting the same with substantially 90% caustic potash in amount substantially two (2) times the Weightofthe ore and an equal Weight of Water, thus obtaining Water soluble potassium silicate and potassium aluminate and Water insoluble but acid soluble potassium aluminum silicate; diluting the alkali digestion products With an amount of Water at least equal in volume to said products, and carbonating with carbon dioxide to remove the Water soluble potassium values; repeatedly filtering and Washing the carbonation products, the Wash Water requirements .being from 2.25 to 4.5 gallons of Water per pound of ore utilized; digesting the alumina and silica residue with from to 125% excessof substantially 95% sulphuric acid to remove the aluminum as soluble salts;` and ltering and fractionally crystallizing the aluminum solution, thus obtaining as a first fraction practically pure alum (K,SO4Al2(SO4)3.24H2O) and successive fractions of alum containing increasing quantities of aluminum sulphate.

Signed by me this lith day of May, 1922.

Y SHERMAN W. SCOFIELD.

4Signed by me' this 13th day of May, 1922.

JOHN B. LA RUE. 

